1. Field of the Invention
This invention relates to a watertight key unit for an electronic device.
2. Description of the Related Art
FIG. 1 illustrates a conventional personal digital assistant (PDA) 11 that includes a housing with a top cover 111, and a printed circuit board (not shown) mounted in the housing. A plurality of switches (not shown) are electrically connected to the printed circuit board for providing key input functions, such as arrow keys (i.e., left, right, forward and backward keys, enter key, etc.). The top cover 111 is formed with a plurality of holes 1111. A key unit is mounted on the top cover ill, and includes a plurality of keys 12 that respectively extend through the holes 1111, and that are respectively coupled to the switches (not shown) on the printed circuit board for operating the switches. Each of the keys 12 is made from an elastic material, such as rubber, which permits watertight contact between the key 12 and the top cover 111. However, a large spacing is required between two adjacent ones of the keys 12 for facilitating manufacturing of the PDA 11, which is unfavorable in view of current trends toward miniaturization of the PDA 11. In addition, assembly of the keys 12 is time-consuming, which results in an increase in manufacturing costs.
FIGS. 2 and 3 illustrate another conventional PDA 21 that includes a housing, a printed circuit board 212 mounted in the housing, a four-way micro stick switch 213 coupled electrically to the printed circuit board 212 for providing left, right, forward, and backward key input functions, and a multifunctional key 22 mounted on a top cover 211 of the housing and connected to the micro stick switch 213. The top cover 211 is formed with a hole 2111 for extension of the multifunctional key 22 therethrough. A gap 20 is required to be formed between the multifunctional key 22 and a hole-defining wall that defines the hole 2111 so as to permit operation of the multifunctional key 22 and the micro stick switch 213. By integrating the left, right, forward, and backward key input functions into an assembly of the multifunctional key 22 and the micro stick switch 213, the aforesaid drawbacks of the conventional PDA 11 of FIG. 1 can be avoided. However, the multifunctional key 22 of the conventional PDA 21 is non-watertight due to the presence of the gap 20. As a consequence, the printed circuit board 212 of the conventional PDA 21 may be damaged by water when water accidentally enters through the gap 20 and into the housing of the PDA 21.